1. Field of the Invention
The present invention relates to a technique for displaying an image on a display device after subjecting the image being captured to image processing for emphasizing an edge component in the image, to assist users in adjusting the focus during shooting.
2. Description of the Related Art
In general, a photographer checks an image being captured and displayed on a display device such as an electronic viewfinder (EVF) attached to an image pickup apparatus in focusing on a subject during shooting. One way of assisting this focusing is peaking display, which is a technique for displaying an image with an emphasized edge component or displaying an image with a colored edge component as discussed in Japanese Patent Application Laid-Open No. 2010-50592. A photographer can recognize the degree of in-focus by checking an image displayed by means of the peaking display.
In recent years, image pickup elements capable of picking up images at a 4K resolution (3840×2160 pixels) have become available and have evolved into shooting systems capable of handling finer images. Meanwhile, display devices such as an EVF attached to an image pickup apparatus have not been improved to the extent to display such images at fine resolution as compared with the image pickup elements, and often use resolutions on the level of only quarter high definition (qHD) (960×540 pixels).
FIGS. 3A and 3B are diagrams illustrating frequency characteristics related to image processing in a conventional image pickup apparatus. Area A of FIG. 3A indicates, for example, a frequency band of an image captured in 4K resolution, and areas B of FIGS. 3A and 3B indicate, for example, a frequency band of an image that can be displayed in a display device of qHD resolution. As apparent from FIGS. 3A and 3B, when the resolution of the display device is lower than the resolution of the image pickup apparatus, it is necessary to perform resolution conversion so that the resolution of a captured image is reduced to match with the resolution of the display device.
In a process of the resolution conversion in the conventional image pickup apparatus, a high-frequency edge component included in a captured image disappears in a filtering process and therefore, the peaking display cannot be appropriately performed. It may be conceivable to thin an extracted high-frequency edge component and display the thinned image on a display device having a low resolution. However, aliasing occurs due to the thinning.